Technical Key Points of PE Injection Molding
1. Raw Material Preparation and Selection
1.1 Material Selection
Different types of PE are selected based on product usage: HDPE with high crystallinity and rigidity is suitable for industrial parts and pipes; LDPE with good flexibility and transparency is used for injection-molded containers and daily necessities; LLDPE, which balances toughness and strength, is ideal for heavy-duty packaging. The melt flow rate is a key indicator, with high-flow grades for thin-walled complex products and medium-low flow grades for thick-walled products.
1.2 Raw Material PreprocessingPE has low hygroscopicity, so no drying is required under normal conditions. However, damp materials need to be dried at 70-90℃ for 2-4 hours to reduce moisture content below 0.2% and avoid bubble defects. Before feeding, raw materials are screened to remove agglomerates and impurities, preventing damage to equipment and ensuring product quality.
2. Core Injection Molding Control
2.1 Process Parameter Setting
The barrel temperature is controlled in sections within 160-220℃, with higher temperatures for HDPE to ensure full melting and slightly lower temperatures for LDPE to avoid over-melting. The injection pressure ranges from 80-150MPa, and the holding pressure is 50%-70% of the injection pressure. The cooling time is 20-60 seconds, ensuring the product is fully solidified before demolding.
3. Mold Adaptation Technology
3.1 Mold Structure Design
The gating system is designed to match PE’s low viscosity and high fluidity, with a main runner taper of 1:5-1:7 and circular or trapezoidal sub-runners. The exhaust gap is set at 0.01-0.02mm to ensure smooth gas discharge. For thick-walled products, a reasonable shrinkage allowance is reserved in the mold cavity, with HDPE requiring a higher shrinkage rate than LDPE.
3.2 Mold Material and MaintenanceMold cavities and cores are made of wear-resistant alloy steel, with pre-hardened steel for ordinary products and mirror stainless steel for high-precision products. The mold surface is polished to a roughness of Ra ≤ 0.4μm to improve product appearance. Regular maintenance includes cleaning cavity residues, checking the lubrication of guide mechanisms, and ensuring unobstructed cooling channels.
4. Post-Processing and Quality Control
4.1 Product Post-Processing
After molding, gates, flashes, and burrs are removed, with manual trimming for small batches and specialized equipment for mass production. High-precision products are annealed at 60-80℃ for 1-2 hours to eliminate internal stress and improve dimensional stability.
Summary
PE injection molding requires full-process control from raw material selection to quality inspection. The key is to optimize process parameters based on PE types and use reasonable mold structures to ensure product quality. Through standardized technical management, the performance advantages of PE can be fully utilized, production efficiency improved, and the needs of various application fields met.
